The printed circuit boards now in use are made from organic materials. These materials limit the properties of the board. For example, when integrated circuit chips are disposed on the boards, and are connected electrically to the boards, the chips have a significantly lower coefficient of thermal expansion than the boards. This limits the temperature range to which the integrated circuit chips and the boards can be subjected. At temperatures above such ranges, the board tends to expand significantly relative to the chips that the electrical connections between the chips and the boards tend to become interrupted. This has been particularly true in recent years because the size of the integrated circuit chips has been progressively reduced without significantly reducing the heat generated in the chip. As a result, the temperatures produced in many chips have progressively increased and have produced hot spots in the printed circuit board at the positions where the chips tend to be electrically connected to the printed circuit boards. This has aggravated the tendency for the chips to become disconnected electrically from the printed circuit boards.
The temperatures generated in the chips also present another problem. Since the printed circuit boards are made from an organic material, their properties deteriorate at elevated temperatures. The temperatures generated in the chips produce hot spots on the board. These hot spots cause the properties of the boards at such hot spots to degenerate. These hot spots sometimes causes the printed circuit boards to melt at such hot spots. The heat cannot be dissipated by the printed circuit board and therefore adversely effects the life of the chip.
The printed circuit boards now in use also have other significant disadvantages. For example, since the boards are made from organic materials, they can be exposed to manufacturing processes only in limited temperature ranges without damaging their properties. This has prevented layers on the printed circuit boards from being doped to produce alloys with modified electrical resistances. The reason is that the doping of such layers has to occur at high relatively temperatures or imposes ion bombardment that damages organic resins. As a result, electrical resistances have had to be adjusted by pattern geometry techiques. This has considerably increased the planar space which has had to be occupied by the circuitry including the modified total resistance geometry structures.
There is another significant disadvantage in the printed circuit boards now in use, particularly when the boards have multiple layers of electrical circuitry. In these boards, electrical connections between adjacent layers are provided by producing holes in the dielectric layers between the electrically conductive layers and by plating with an electrically conductive material the surfaces defining the holes. This has produced an increase in the number of steps required to produce the printed circuit board, thereby increasing the cost of producing the boards and decreasing the rate at which the boards can be produced. Plating deposition defects and the high mismatches experienced in the coefficient of thermal expansion with multilayer printed circuit boards have led to reduced production yields and increased in service failure rates.